Method for creating the high voltage complementary BJT with lateral collector on bulk substrate with resurf effect

ABSTRACT

Complementary high-voltage bipolar transistors formed in standard bulk silicon integrated circuits are disclosed. In one disclosed embodiment, collector regions are formed in an epitaxial silicon layer. Base regions and emitters are disposed over the collector region. An n-type region is formed under collector region by implanting donor impurities into a p-substrate for the PNP transistor and implanting acceptor impurities into the p-substrate for the NPN transistor prior to depositing the collector epitaxial regions. Later in the process flow these n-type and p-type regions are connected to the top of the die by a deep n+ and p+ wells respectively. The n-type well is then coupled to VCC while the p-type well is coupled to GND, providing laterally depleted portions of the PNP and NPN collector regions and hence, increasing their BVs.

FIELD OF THE INVENTION

This invention is in the field of bipolar transistor fabrication, and is more specifically directed to the fabrication of complementary transistors having varying characteristics on a common substrate using bulk silicon technology.

BACKGROUND OF THE INVENTION

Integrated circuits have utilized bipolar junction transistors for many years, taking advantage of their high gain characteristics to satisfy high performance and high current drive needs. In particular, as is well known in the art, bipolar transistors are especially well-suited for high frequency applications, such as now used in wireless communications.

Silicon-on-insulator (SOI) technology is also well-known in the art as providing important advantages in high-frequency electronic devices. As is fundamental in SOI technology, active devices such as transistors are formed in single-crystal silicon layers formed over an insulator layer, such as a layer of silicon dioxide commonly referred to as buried oxide (BOX). The buried oxide layer isolates the active devices from the underlying substrate, effectively eliminating parasitic nonlinear junction capacitances to the substrate and reducing collector-to-substrate capacitances. To the extent that high frequency performance of bulk transistors was limited by substrate capacitance, SOI technology provides significant improvement.

Record f_(T)peak*BV_(CEO) product has been achieved for both NPN and PNP. This was possible due to re-surf effect from the substrate through buried oxide on low-doped collector region.

However, high cost of SOI substrates prohibit mass product development using this technology. In addition, a split voltage source is required to implement re-surf effect in PNP (for a grounded substrate). It has also been observed that significant self-heating occurs at currents above f_(T)peak and large V_(CE).

A conventional SOI bipolar transistor is designed to be a high performance device. However, a high performance transistor is somewhat limited by its construction, from a standpoint of both breakdown voltage and performance. As is fundamental in the art, the collector emitter breakdown voltage (BVCEO) depends upon the thickness of collector region and upon the doping concentration of the collector region. Lighter doping of the collector region and a thicker collector region would increase this breakdown voltage.

In real circuits, the emitter and bases complementary SiGe bipolar junction transistor (BJTs) are biased around the highest potential Vcc (relative to grounded substrate) while the collectors are switched between Vcc and 0. High B-C bias corresponds to zero potential at collector.

What is needed is a method of increasing PNP BV without decreasing collector doping concentration or increasing collector region thickness of the PNP while including a high voltage NPN on the same bulk processed circuit/substrate.

SUMMARY OF THE INVENTION

The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention, nor to delineate the scope thereof. Rather, the primary purpose of the summary is to present some concepts of the invention in a simplified form as a prelude to a more detailed description that is presented later.

In accordance with an embodiment of the present application, an integrated circuit structure, the integrated circuit structure comprising: complementary PNP and NPN structures; wherein the PNP and NPN structures include a p-type bulk semiconductor substrate; PNP and NPN active device regions; buried N+ and P+ resurf regions; wherein both the p-type region and the active device PNP and NPN regions are implemented with single-crystal silicon; and deep trench isolation regions surrounding each transistor, wherein the deep trench isolation regions isolate the complementary PNP and NPN structures from each other.

In accordance with another embodiment of the present application, a method of forming complementary PNP and NPN structures, the method of forming complementary PNP and NPN structures comprising: providing a p-type bulk semiconductor substrate; creating PNP and NPN active device regions; implanting buried N+ and P+ resurf regions in the PNP and NPN device regions respectively; implementing both the bulk semiconductor substrate and PNP and NPN device regions with single-crystal silicon; and surrounding each transistor with deep trench isolation regions to isolate the complementary PNP and NPN structures from each other.

DESCRIPTION OF THE VIEWS OF THE DRAWING

FIG. 1A illustrates a cross-section of an embodiment of the present invention.

FIG. 1B illustrates an enlarged portion of FIG. 1A detailing the PNP transistor.

FIG. 1C illustrates an enlarged portion of FIG. 1A detailing the NPN transistor.

FIG. 2 shows the dependency of BV_(CER) on the collector doping level of the PNP for various base-collector spacings SBC in μm.

FIG. 3 shows the dependency of BV_(CER) on the collector doping level of the NPN for various base-collector spacings SBC in μm.

FIG. 4 shows the dependency of BV_(CER) on for various base-collector spacings SBC in μm for both NPNs and PNPs.

In the drawings, like reference numerals are sometimes used to designate like structural elements. It should also be appreciated that the depictions in the figures are diagrammatic and not to scale.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The present invention is described with reference to the attached figures. The figures are not drawn to scale and they are provided merely to illustrate the invention. Several aspects of the invention are described below with reference to example applications for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide an understanding of the invention. One skilled in the relevant art, however, will readily recognize that the invention can be practiced without one or more of the specific details or with other methods. In other instances, well-known structures or operations are not shown in detail to avoid obscuring the invention. The present invention is not limited by the illustrated ordering of acts or events, as some acts may occur in different orders and/or concurrently with other acts or events. Furthermore, not all illustrated acts or events are required to implement a methodology in accordance with the present invention.

In an embodiment of the present invention is shown in FIGS. 1A-1C, the complementary PNP 100 and NPN 200 structures include on a common substrate using bulk silicon technology, having a p-type region 101, active device regions 104 and 204 respectively. The initial doping level of the active device regions 104 and 204 can be n-type, 1e14. In the present example, both the p-type region 101 and the active device regions 104 and 204 are implemented with single-crystal silicon. To create a structure that has higher PNP BV FIG. 3B, a buried n-type resurf region 106 is included under the active device region 104 of the PNP transistor 100, by implanting donor impurities of about 3e16 to 3e18 1/cm3 p-type region 101 prior to collector 104 epitaxial growth. Later in the process flow this n-type region 106 is connected from the top by deep n-type well 110 and is biased at Vcc. In this case it will deplete lateral portions of the PNP collector region and hence, will increase its BV. To create a structure that has higher NPN BV FIG. 3C, a buried p-type resurf region 206 is included under the active device region 204 of the NPN transistor 100, by implanting accepter impurities of about 3e16 to 3e18 1/cm3 into p-type region 101 prior to collector 204 epitaxial growth. Later in the process flow this p-type region 206 is connected from the top by deep p-type well 210 and is biased at GND. In this case it will deplete lateral portions of both the NPN collector region and hence, will increase its BV.

The structure providing a PNP transistor 100 with a higher BV (FIG. 1B) is described below.

First, standard p-type bulk wafer is provided as described in the present invention as shown in FIGS. 1A-1B.

Next, a first masking and implant step is accomplished to implant a high 3e16 to 3e18 1/cm3 dose of n-type species. The highly doped n-layer 106 is vertically under the PNP.

Next, collector 104 epi is grown with very low doping <3e14 1/cm3 and thickness ˜3 to 4 um.

A Third masking and etching step is accomplished to provide a hard mask for defining and for deposition of an insulator layer STI 105 in the active device region 104.

Deep trenches 109 are formed, to encircle the PNP transistor 100 and the deep n-type well 110. The trenches extend from the top of the die to the below of the highly doped n-layer 106 and the deep n-type well extends from the top of the die to and through the active device area 104 extending into the highly doped n-layer 106, wherein the deep n-type well 110 touches the implanted highly doped n-layer and extends to the top of the die providing a top contact to the implanted n-layer 106.

A base epitaxial semiconductor layer 113 is deposited, defined and doped with an impurity of the opposite conductivity type on top of the active device region 104 with base contacts 111 coupled thereto. The separation between the base area exposed by the shallow trench isolation STI 105 and p-well 107 is critical in determining the BV_(CER) and f_(T)peak of the PNP transistor as shown in FIG. 4.

And finally, an emitter region 108 covers a portion of the base epitaxial semiconductor layer 113, wherein the emitter region 108 is highly doped with the same conductivity type as the active device region 104.

The structure providing a NPN transistor 200 with a higher BV (FIG. 1C) is described below.

First, standard p-type bulk wafer is provided as described in the present invention as shown in FIGS. 1A and 1C.

Next, a first masking and implant step is accomplished to implant a high 3e16 to 3e18 1/cm3 dose of p-type species. The highly doped p-layer 206 is vertically under the NPN.

Next, collector 204 epi is grown with very low doping <3e14 1/cm3 and thickness ˜3 to 4 um.

A Third masking and etching step is accomplished to provide a hard mask for defining and for deposition of an insulator layer STI 105 in the active device region 204.

Deep trenches 109 are formed, to encircle the NPN transistor 200 and the deep p-type well 210. The trenches extend from the top of the die to the below of the highly doped p-layer 206 and the deep p-type well extends from the top of the die to and through the active device area 204 extending into the highly doped p-layer 206, wherein the deep p-type well 210 touches the implanted highly doped p-layer and extends to the top of the die providing a top contact to the implanted p-layer 206.

A base epitaxial semiconductor layer 213 is deposited, defined and doped with an impurity of the opposite conductivity type on top of the active device region 204 with base contacts 111 coupled thereto. The separation between the base area exposed by the shallow trench isolation STI 105 and n-well 207 is critical in determining the BV_(CER) and f_(T)peak of the NPN transistor as shown in FIG. 4.

And finally, an emitter region 208 covers a portion of the base epitaxial semiconductor layer 213, wherein the emitter region 208 is highly doped with the same conductivity type as the active device region 204.

The base epitaxial semiconductor for the NPN and the PNP can be either SiGe or silicon. The base epitaxial semiconductor can also be deposited in two operations, one for the NPN and one for the PNP.

FIG. 2 shows the dependency of BV_(CER) on the collector doping level of the PNP for various base-collector spacings SBC in μm. Numbers aligned with the curves denote base-collector spacing in μm.

FIG. 3 shows the dependency of BV_(CER) on the collector doping level of the NPN for various base-collector spacings SBC in μm. Numbers aligned with the curves denote base-collector spacing in μm.

FIG. 4 shows the dependency of BV_(CER) on for various base-collector spacings SBC in μm for both NPNs and PNPs. Collector doping is 3e15 for the PNP and 2e15 for the NPN.

The present invention offers three advantages over existing SOI architectures:

-   -   (1) The process flow starts with cheap standard bulk wafer.     -   (2) Proper bias can be applied to PNP and NPN buried layers to         use re-surf effect to its full strength. According to TCAD         results, similar f_(T)peak*BV_(CEO) numbers compared to devices         on SOI can be achieved.     -   (3) Self-heating will be much lower.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only and not limitation. Numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the spirit or scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above described embodiments. Rather, the scope of the invention should be defined in accordance with the following claims and their equivalents. 

What is claimed is:
 1. A method of forming complementary PNP and NPN structures comprising: providing a p-type bulk semiconductor substrate; creating PNP and NPN active device regions; implanting buried N+ and P+ resurf regions in the PNP and NPN device regions respectively; implementing both the bulk semiconductor substrate and PNP and NPN device regions with single-crystal silicon; surrounding each transistor with deep trench isolation regions to isolate the complementary PNP and NPN structures from each other; performing a first masking operation and implanting a highly doped n-layer in the p-type bulk semiconductor substrate, wherein the highly doped n-layer is vertically under the PNP area and extends toward and touching the deep trench isolation; performing a second masking operation and implanting step performed after Pad Oxidation, before Nitride deposition to create a uniform collector doping level in the active device region; performing a third masking operation and etching step to provide a hard mask for defining a region of a shallow trench insulation layer STI in the active device region; forming deep trenches isolations, to encircle the PNP transistor and the highly doped n-layer, wherein the trenches extend below the bottom of the highly doped n-layer and extend to the top of die; implanting a p-type well extending through the STI layer and touching the collector of the active device layer with a collector contact coupled thereto; implanting a deep n-type well extending from the top of the wafer through the STI layer and the active device layer, touching the highly doped n-layer with a VCC contact coupled thereto; depositing a base epitaxial semiconductor layer, defining and doping with an impurity of the opposite conductivity type on top of the active device region with a base contact coupled thereto; and depositing an emitter region that covers a portion of the base epitaxial semiconductor layer, wherein the emitter region is highly doped with the same conductivity type as the active device region.
 2. The method of forming complementary PNP and NPN structures of claim 1, wherein the PNP active device region has an acceptor doping of <3e14 1/cm3 and thickness of 3 to 4 um.
 3. The method of forming complementary PNP and NPN structures of claim 1, wherein the buried N+ resurf region in the PNP area is implanted with a donor dose of 3e16 to 3e18 1/cm3.
 4. The method of forming complementary PNP and NPN structures of claim 1, wherein the NPN further comprises: performing a fourth masking operation and implanting a highly doped p-layer in the p-type bulk semiconductor substrate, wherein the highly doped p-layer is vertically under the NPN area and extends toward and touching the deep trench isolation; performing a fifth masking operation and implanting step performed after Pad Oxidation, before Nitride deposition to create a uniform collector doping level in the active device region; performing a sixth masking operation and etching step to provide a hard mask for defining a region of a shallow trench insulation layer STI in the active device region; forming deep trenches isolations, to encircle the NPN transistor and the highly doped p-layer, wherein the trenches extend below the bottom of the highly doped p-layer and extend to the top of die; implanting a n-type well extending through the STI layer and touching the collector of the active device layer with a collector contact coupled thereto; implanting a deep p-type well extending from the top of the wafer through the STI layer and the active device layer, touching the highly doped p-layer with a GND contact coupled thereto; depositing a base epitaxial semiconductor layer, defining and doping with an impurity of the opposite conductivity type on top of the active device region with a base contact coupled thereto; and depositing an emitter region that covers a portion of the base epitaxial semiconductor layer, wherein the emitter region is highly doped with the same conductivity type as the active device region.
 5. The method of forming complementary PNP and NPN structures of claim 1, wherein the NPN active device region has a donor doping of <3e14 1/cm3 and thickness of 3 to 4 um.
 6. The method of forming complementary PNP and NPN structures of claim 1, wherein the buried P+ resurf region in the NPN area is implanted with an acceptor dose of 3e16 to 3e18 1/cm3.
 7. The method of claim 1, wherein the buried N+ resurf region included under the PNP transistor and the buried P+ resurf region under the NPN are coupled to the top of the wafer by deep n-type and p-type wells respectively and are biased at Vcc and GND respectively, wherein the biases will deplete lateral portions of both the PNP and NPN collector regions and hence, will increase their BVs. 